Just out of Curiousity... Carbon

Most Jump bikes used to have steel frames (and bloody heavy ones as well), I suspect that has changed now.

I doubt it.

As Hippy's link say a carbon frame could be made that would be strong enough and repaired when things go wrong but most people jumping would want a bike that mag get a little bent and still be ridden for a bit rather than need repairing e.t.c People using jump biek would tend to want to bash them about a fair bit in general and not have to worry about repairing small damages. That's what I reckon anyway.